This invention relates to a portable machine tool, and particularly, but not exclusively, to a tool for in situ repair of large check valves.
A known type of check valve is shown in FIG. 1 of the accompanying drawings. This check valve comprises a valve body 2 defining an inlet 4 and an outlet 8 that communicate by way of a valve cavity 10. The valve body includes a seat member 14 defining a valve seat 16. The external surface of seat member 14 is cylindrical and is coaxial with inlet 4 and outlet 8. A flapper 18 is mounted to pivot relative to valve body 2 about a pivot pin 22 that extends through a horizontal bore in valve body 2. The valve body defines an access passage 26, which is normally closed by a cover plate 30 that is secured to the valve body by bolts 32.
When the pressure of fluid at the inlet 4 is higher that the pressure of fluid at the outlet 8, flapper 18 is pivoted in the counterclockwise direction, away from seat 16 and allows flow of fluid from inlet 4 towards outlet 8. The valve body is formed with a stop 34 to limit pivotal movement of the flapper in the counterclockwise direction. If the pressure at outlet 8 should exceed the pressure at inlet 4, flapper 18 is forced into seating engagement with seat 16 and prevents flow in the reverse direction
It is necessary from time to time to repair valves of the kind shown in FIG. 1. One of the repair operations involves removing the valve seat member 14 so that a new seat member can be installed. This may be accomplished by mounting a machining head inside the valve cavity. A cutting element is supported relative to the machining head and is connected to drive motors so that it is able to be rotated about the common axis 36 of the inlet and outlet and can be fed radially (R) and longitudinally (Z) relative to axis 36. The limited space available in the valve cavity effectively requires that the motors for driving the machining head be disposed outside the valve cavity and connected to the cutting element through a transmission mechanism that extends through the access passage 26.
In some applications it is desirable that the machining head be positioned inside the valve cavity without need for personnel to enter the valve cavity. Therefore, it is desirable to mount the machine tool from the exterior of the valve body.
One possible solution would be to mount the machining head to a support structure that extends through the access passage in a manner such as to prevent movement of the machining head relative to the support structure in the Z direction, and advance the machining head in the Z direction by moving the support structure in the Z direction. However, the limited range of movement between the stop 34 and the opposite side of the access passage limits the feed that can be accomplished.
Alternatively, the support structure may be mounted stationarily to the valve body and universal joints employed to accommodate shift of the machining head relative to the drive motors.